Radio Frequency (RF) and microwave signals and components are employed in a variety of devices, including mobile communication devices such as mobile telephones and communication test equipment. One type of commonly employed RF component is a passive signal splitter or power divider which is may be used to split or divide an RF or microwave signal and provide the divided signal to two or more output ports. Passive signal splitters often can also be used as a signal combiner. Such devices are sometimes referred to as reciprocal devices. The terms “signal splitter,” “signal combiner,” “power splitter,” and “power combiner” are sometimes used interchangeably with respect to such devices.
A number of different parameters are used to define the performance of a signal splitter. Among these parameters are insertion loss, port isolation, input impedance match (e.g., input return loss), and output impedance match (e.g., output return loss)—all of which can be characterized as a function of an operating frequency range. Other characteristics which are often important include size, component and manufacturing loss, repeatability, and reliability.
One application for such a signal splitter is in a test system which may be used to combine and/or split transmit and receive signals in the RF and microwave frequency bands. In some test systems, it may be desired or necessary to test signals over a wide range of frequencies. For example, in one particular system, it is desired to test signals over a frequency range extending from below VHF (e.g., 10 MHz), up to 6 GHz.
Lumped or discrete element signal splitters have been produced which can operate well at the lower end of this frequency range, but their performance degrades at higher frequencies (e.g., above 2.5 GHz). Meanwhile, Wilkinson power splitters have been produced which can operate well at the higher end of this frequency range, but their performance degrades at lower frequencies (e.g., below 400 MHz). Wilkinson splitters have practical size limitations and become very large below VHF frequencies.
What is needed, therefore, is a signal splitter that can provide acceptable performance characteristics over a very wide bandwidth.